PV Loop calculates most of these parameters, but because the regression equations are in a different form, some of the values have to be converted so that they are comparable with the values calculated by PVAN.
The conversion equation for each parameter is described in the last part of this solution, but first we'll cover Emax and Goodness of Fit.
Emax
Emax refers to a parameter that is calculated during a time-varying elastance analysis, however PV Loop doesn't currently perform this type of analysis.
(If you think this would be a popular feature we would be interested in hearing.)
Goodness of fit
Some of these parameters are referring to the goodness of fit of a regression (listed below). In PVAN these values are labelled r, which may be correlation coefficients, although the PVAN user guide does not describe how they are calculated.
PV Loop uses the standard R-squared (coefficient of determination) measure for goodness of fit. This measure works with both linear and non-linear fits, and in the linear case is the square of the correlation coefficient.
The following sections explain how to get values from PV Loop that are comparable to PVAN's occlusion parameters. PVAN is inconsistent in the naming of its parameters, and in the form it uses for equations, which unfortunately makes these instructions repetitious.
Parameters of a Linear ESPVR Regression
Open a PV Loop data analysis selection in the Loop View and ensure that ESPVR is enabled and that linear is selected in the drop down.
The ESPVR equation is shown in the legend in the form: a * Ves + b from which you can calculate the following:
- Ees = a
- V0 = -b / a
- r-ESPVR = goodness of fit
Parameters of a Linear EDPVR Regression
Open a PV Loop data analysis selection in the Loop View and ensure that EDPVR is enabled and that linear is selected in the drop down.
The EDPVR equation is shown in the legend in the form: a * Ved + b from which you can calculate the following:
- slope-EDPVR = a
- int-EDPVR = b
- r-EDPVRlin = goodness of fit
Parameters of an Exponential EDPVR Regression
Open a PV Loop data analysis selection in the Loop View and ensure that EDPVR is enabled and that exponential is selected in the drop down.
The EDPVR equation is shown in the legend in the form: a * exp(b * Ved) from which you can calculate the following:
- k1-EDPVR = b
- k2-EDPVR = a
- r-EDPVRlin = goodness of fit
Parameters of the PRSW Regression
Open a PV Loop data analysis selection in the PRSW plot.
The equation in the legend is in the form: a * Ved + b from which you can calculate the following:
- PRSW = a
- PRSW0 = -b / a
- R-PRSW = goodness of fit
Parameters of the dP/dt Max vs EDV Regression
Open a PV Loop data analysis selection in the dP/dt Max vs EDV plot.
The equation in the legend is in the form: a * Ved + b from which you can calculate the following:
- dPdt - EDV = a
- dPdt - EDV intercept = -b / a
- r dPdt-EDV = goodness of fit
For further technical assistance with this or any other issue, please contact ADInstruments Technical Support by clicking HERE.